1. Field of the Invention
The invention relates in general to a paper-width detecting device of a document feeder, and more particularly to a paper-width detecting device having the function for detecting the width of non-standard paper.
2. Description of the Related Art
Referring to FIG. 1, a partial top view of a conventional automatic document feeder is shown. In FIG. 1, an automatic document feeder 10 includes a paper tray 12, a paper guide 13 and sensing elements 14a, 14b and 14c, wherein the paper guide 13 is fixed on the paper tray 12 for accommodating papers 15a, 15b and 15c. The sensing elements 14a to 14b are separately disposed on the paper tray 12 for correspondingly detecting the width of the papers 15a to 15c. When the paper 15a covers up the sensing element 14a, the sensing element 14a detects the paper 15a, and the automatic document feeder 10 will preset the width of the paper 15a as A5 width. Besides, when the paper 15b covers up the sensing elements 14a and 14b but not the sensing element 14c, the width of the paper 15b is preset as A4 width. When the paper 15c covers up the sensing elements 14a to 14c, the width of the paper 15b is preset as B4 width, in accordance with the positions of the sensors 14a to 14c covered up by the paper 15c. 
It is noteworthy that the conventional design of using a plurality of sensing elements to detect paper width can be applied to standard paper sizes such as A5, A4 and B4 only, and cannot detect the width of non-standard paper. Moreover, if more types of paper width are to be detected, more sensing elements and more complicated paper-width determining mechanism need to be disposed in the automatic document feeder. Consequently, additional costs will be incurred.